The immunological destruction of blood cells may result when the membrane of the cell is altered by antibody, reacting with cell-bound antigens, or complement. We wish to investigate the role of each of the components of the humoral immune system in the destruction of the cells of patients with neoplastic disease. In particular, we wish to determine the role of antigens, particularly glycoprotein antigens, and the effect of their placement in the membrane in modifying interaction with antibody, the role of antibodies and their particular molecular structure and immunoglobulin class and sub-class in effecting lysis, and the role of complement and its activation by antibody or by the alternate pathway in the lysis of blood cells (red cells, white cells and platelets) in patients with hematological diseases, especially malignant ones. In particular, we wish to define and assess the role of membrane abnormalities present in many patients with myeloproliferative diseases upon the interaction of antigen, antibody and complement. From these studies, we hope to gain more understanding about the destruction of cells by immune processes and insight into the ways in which this may be modified.